Atypical

Nothing here shares a mechanism with anything else here. A substance lands in Atypical when its pharmacology is understood well enough to describe and simply has no populated neighbours on this tree — salvinorin A is a selective κ-opioid agonist, muscimol a GABA-A agonist, ibogaine a multi-receptor agent with a cardiac liability of its own. Read each family on its own terms; nothing generalises from one to the next, and the subject-level Harm Reduction and Receptors pages here are necessarily thinner than a real class's.

Two families are filed by something other than pharmacology, and both are deliberate: Inhalants is grouped by route and Adulterants by role, because in each case that is what carries the risk. Those are the only two exceptions, and a third would need an argument of the same shape. Atypical is not Misc: if the mechanism is unknown rather than merely unaccompanied, the substance belongs there instead.